1. Field of the Invention
The present invention relates to a miniature circuit breaker and, more specifically, to a miniature circuit breaker having an arc fault detector structured to actuate a shape memory alloy element coupled to a trip device.
2. Background Information
Miniature circuit breakers are used in devices with limited space and/or weight limitations, such as, but not limited to, aircraft. A miniature circuit breaker has the typical circuit breaker components, such as a non-conductive housing, an external actuator, at least two external terminals structured to be coupled to a line and a load, a pair of separable contacts including a first, stationary contact electrically coupled to one external terminal and a second, movable contact couple to the other external contact, an operating mechanism structured to move the separable contacts between a first, closed position wherein the contacts engage each other and a second position, wherein the contacts are separated, and a trip device structured to latch the operating mechanism in the first position until an over-current condition occurs. The operating mechanism has a spring biasing the separable contacts to the second position. Thus, when the trip device is actuated, the latch releases the operating mechanism and the separable contacts move to the second position. The operating mechanism is further coupled to the external actuator. The external actuator is structured to move the separable contacts to the first position after a trip event, or may be used to manually separate the contacts.
In the prior art, a circuit breaker having arc fault protection included a trip device with at least two tripping mechanisms; one mechanism for an over-current situation and one mechanism for an arc fault on the load side of the circuit breaker. The over-current mechanism typically included an elongated bimetal element that would bend in response to temperature changes. The act of bending actuated the latch thereby allowing the operating mechanism to separate the separable contacts. Heat is created in response to current passing through the bimetal element. Thus, the greater the amount of current, the greater the degree of bending. The electronic arc fault mechanism included an electronic arc fault detector and a solenoid assembly. When the electronic arc fault detector sensed an arc, a pulse was sent to the solenoid and the solenoid actuated the trip device. The disadvantage to the electronic arc fault mechanism is that the solenoid is a relatively large mechanism that requires additional space.
There is, therefore, a need for a smaller mechanism structured to activate the trip device in the event of an arc fault.
There is a further need for a miniature circuit breaker able to detect and trip in the event of an arc fault.